1. Field of the Invention
The present invention relates to a technique to recode gray information and sector information into a servo frame region formed on a magnetic disk.
2. Description of the Related Art
Accompanying drawings FIGS. 15(a) and 15(b) illustrate a configuration of a conventional magnetic disk; FIG. 15(a) schematically illustrates a configuration of a conventional magnetic disk and FIG. 15(b) schematically shows a configuration of a servo frame formed on the magnetic disk of FIG. 15(a).
A conventional magnetic disk 110, as shown in FIG. 15(a), takes the form of a platter one side or the both sides of which serve recording layer covered with a magnetic material, and a non-illustrated magnetic head reads information from and write information into a surface (a storage region) of the magnetic disk 110.
On the magnetic disk 110, a number of servo frames 111 are radially formed so as to stretch from the center to the circumference at predetermined intervals. Information for specifying a magnetic head is recorded in a servo frame 111.
For example, each servo frame 111 of a conventional magnetic disk 110 retains a preamble, a servo mark, gray/sector information (head information), a position burst, a post code and other information.
An exemplary gray/sector information is 24 bit formed by 16-bit gray information and 8-bit sector information, and a servo frame 111 prepares a space for retaining such gray information and sector information therein.
Here, gray information is a gray code generated by logical conversion performed on binary data representing a cylinder number, and sector information is binary data representing a sector number.
A magnetic disk apparatus reads data from a magnetic disk 110 with reference to gray information and sector information recorded in a servo frame with the intention of preventing a servo-frame shift and/or a track shift, which may destroy user data, from occurring.
A data recoding density has been enhanced year by year and accordingly, a servo sample rate (a servo sample frequency) has been getting higher. A raise in a servo sample rate requires an increase in the number of servo frames 111 but such an increase problematically lowers a format efficiency of a magnetic disk 110.
For compatibility between an increase in the number of servo frames and the prevention of lowering in format efficiency of a magnetic disk 110, effective solutions are enhancement of a recording density (a bit density) into a servo frame 111 and reduction in a data amount to be recorded into a servo frame 111.
For example, Japanese Patent Application Laid-Open (KOKAI) No. HEI 8-221892 discloses a manner for saving a storage region space of a disk by coding a servo address so that lesser bits are used for storing the servo address.
On a magnetic disk 110, both of gray information and sector information have to be recorded into a servo frame 111 in order to inhibit a servo-frame shift and/or a track shift. A conventional magnetic disk 110 however requires a long bit length for recording such gray information and sector information, and the data length of a servo frame 111 problematically lengthens. That lowers a format efficiency.